Vibrato organization



May 17, 1949. M. J; LARSEN VIBRAT' ORGANIZATION 5 Sheets-Sheet 1 Original Filed se t. 19. 1944 n J W m L a r150 17.

May 17, 1949. LARSEN 2,470,705

' VIBRATO ORGANIZATION Original Filed Sept; 19. 1944 3 Sheets-Sheet 2 IE:- E

L OW FRIOUGVC Y USO/LIA 70/? FIG-2A gran/who QIbe/vw/{ y M. J. LARSEN 2,470,705

VIBRA'IO ORGANIZATION Original Filed Sept. 19. 1944 3 She'ets-Sheet s C [3/ 'a Z20 Patented May 17, 1949 2,470,705 VIBRATO' ORGANIZATION;

Merwin J. Larsen, Rochester, Ni.;Y'., assignor to Central Commercial Company;- Chicagbfllls; acorporation of Illinois Ori inal. application September 19,- 1944,--,S6iaL-'r No.. 554,837. Divided and thisapplicationJune 27,; 1946,iSeria1l,N0- 679,618 V 3 Claims.

1i This inventionnrelates to: devices for producinayibrato efiectsin the rendition oi; electrically producedomusiclandis a divisional application of myv application for. Electric organ, Ser. No.-

554,837. ,filedjseiptember 19, 1944,: allcwedflMal 9, 19.46.,Tn0WPatent No. 2,403;090; datedJuly 2, 1946'.

An object otthe invention is the production of 1 vibratoetie'cts ,inlmusical sounds resulting from activation ;of a loudspeaker in respo s o transmissionrtheretosof amplified tone signals of musical; irequencr;

A stillliuntherpbject is the provision of means for vD20timing vibrato efifects electronically and foltqcontiiolling the frequency thereof as desired. r object .is ,the provision of means for producing vibratorefiectsin [a system employing;

master; oscillators for controlling operation of generator of 'audio, frequency tone signals,

Another, object .is the provision of means; for producing vibrato-effiectsina tone generating systememplcying stabilized;oscillators operating at predetermined tonefr'equencies corresponding description and *claims taken- :inconnection with the, accompanying drawings in which:

Figure' 1 is a-= diagram: of-: the.-multivibrator stages connected-in: cascade;

Figure 2 and- 2m are: respective: sections, of a, diagram o-f--'-th'e vibrato: connectedwin-a system of-;

frequencygenerators :embodying; a, plurality oi similar:cascadesxotimultivibrato sttl lis, and 5 Figtllle 3: isiaidiagram shcwing theimanner .-theintendedsiorderpofi i'arraneement:of:Fi ur s.- 2';

zmtorfurnish, a; completeeele trical network, em-

h odyingemm improve dqvibrata r Myvimprovedivibrato is primarily adapted ,.for

11562 ins: connection; with; frequency halving. or.

dividing circuits employing space discharge det-- vicesvsuch;lasgoscill-ators on-their equivalent, the

same -iconnected-m cascadeandcontrolled ,by, a,

master oscillator: or: the: equivalent thereof. Multivibratorrstases as-- isc10s d in. the p nde na applicationgoiamyself, James A Oswald and CaxLS- Schionberg; filed September 17, 1943, Ser. .No;. 602,362, nowrPatent No.v2,410,882, dated Novemb.er'.12;.,.1.96, havegiven excellent results, Asmy inventionis designedprimarily f or use with electrical vmusical instruments ,le pl y g; keyin circuits connectedfwith. sources supplying audio signals at the tone frequencies of notes sci. the. even tempered musical scale, twelve cascades 10f; multivibrator stages-will beemployed; such that; stages comprising;onecascade- Will supplyteleo-w trical impulses at ;the tone irequenciesiof fall -Cj notes at; 0ctave-- separation.= Another set of stages will supply electrical impulses at the tone; frequencies -of r all' C#-n0tes at octave separatiom. and so on; to and-inclusive of a setoistages sup plying electrical impulses -at =tone frequencies loft all B notes at octav e--separa tions At Figure 1 pi the -accompanying drawings a C note cascade of; 5 multivibrator stages v and a: master oscillator --are ill ustratecl; the same come-H. prising-stages A; B;-C,D,- E :and F connectedl in cascade -by electrical comppnents soithatstager B oscillates at --afrequency-which is the octavei of stage A; stage-C-operatingaat-a frequency. which -is "the octave of stage Band-1S0 -.on to and inclusive of stage F- which operatesat a ire.- quency-which is the octave of stageflethe masterr control oscillator: Ml y being connectedto, the grid circuit oi the :first 'StEEQ -At' Each of the multivibratorstages includes a a twin triode; inc1uding two sets of electrodes con sist-ing--; of a cathede controle grid,- and plate. The --multivibr-ator A for! example includes :two. sets of associatedelectrodes-including. grid l 3 andplate-l5,' and grid-dband -plate l6. The input. circuit ofthe-twintriodesare completed through high resistance paths oi different effective resists. ances, constituted in the case of control-gridl3a and 1 its associated; cathode -by i-the resistances 4 and 5 and in I the case--ofthe=-control grid- Hi andits associated-cathode,=-by resistancedi The output circuit of the twin triode includes/resistaances' I and *2 leading"iromrplates.I Stand I 6; reel spectively,;with-variable condenser 8 connectedb tween =contrcl grid a l and 1 a :point intermediateresistances I and plate electrode-15; and-inked;- condenser-8; connected betweencontrol grid "1 l3; and-- a point intermediate-plate l Siand resistance 2. The dropping resistance 6 is connected-Ito ap oi-nt= intermediateuresistances a 4; and; Si and leads to the-playingkey 52;: movable-between contacts filland 6i. Contact-.68 returns to'the-i common input circuit =bus :oi trier-several 111111125.,-

vibrators; while contact 61 -lea.ds. .-through gridbiasing resistance-561m ground; thus returning to. thecommon cathodeobusl The resistive in-ultivibraton circuit constituting stage-A is coupled itosthe" succeeding stage B; through the coupling capacitancelslfidhaving the value in the-circuit,illustrated of '20 mmft to the control grid-41 ofone; set :ot thaelecflodes of the twin triode in multivibrator stage B. The twin triode in multivibrator stage B includes two sets of electrodes constituted by control grid l! and plate I9 with an associated cathode, and a control grid [8 and plate 20, with an associated cathode. The control grid [1, which connects to the coupled capacitance It] also completes an input circuit through resistors 23 and 22, returning to the associated cathode. The input circuit for the opposite sets of electrodes is completed from control grid l8 through the resistance 2|, returning to the associated cathode. The resistive paths are of different values as will be hereinafter explained. Dropping resistance E connects to a point intermediate resistances 23 and 22 and leads to the playing key 52 with which is associated the resistance 56'.

The output circuit of the sets of electrodes constituting the twin triode of stage B includes resistances II and [2, connected in each of the plate supply leads and extends to the common plate supply bus. Fixed condenser H is connected to a point intermediate resistance H and plate I9 to control grid 18, while fixed condenser i2 is connected to a point intermediate resistance l2 and plate 20, and to the control grid H. The control grid I8 is connected through coupling capacitance Ill which is of 40 mmf. to the control grid of the first set of electrodes of the twin triode constituting multivibrator stage C.

The circuits for the multivibrator stage C are similar to those described with respect to stages A and B except that the capacity values of condenser H and I2" are of greater value than the corresponding condensers in the preceding stages, as will be hereinafter explained in detail. The biasing circuit is represented as including playing-key 52" connected to resistance 6 with an intermediate point in the low resistance grid circuit. The contact system for the playing key is arranged in a manner similar to that hereinbefore described, where one of the contacts leads to bias resistor 56", returning through ground to the common cathode bus.

Multivibrator stages D, E, and F are coupled through condensers ID", ID and H] of 40 mmf., 40 mmf., and 20 mmf., respectively. The biasing potential on the grid circuits of each of the multivibrator stages D, E, and F is similarly controlled through playing keys 52", 52 and 52 respectively.

Referring to Figures 2 and 2A use is made of master oscillators Ml, M2-Ml2 which are conventional electron-coupled oscillators with the exception that provision is made to vary the frequency thereof. Vacuum tubes made by Radio Corporation of America and identified as type 7A7 have proved satisfactory. There is one of said master oscillators for each individual cascade of multivibrators, the output wave from which is impressed-on the control grid of the first stage of said cascade.

In Figures 2 and 2A a common lead P is adapted to be connected by a resistance R6 to a plate supply source, (not shown), said lead having a large capacitance C6 connected in shunt therewith. Small chokes L2 in the branch circuits PI of common lead P are connected in the plate circuits of respective control tubes VI, V2-Vl2. At X9 is a common lead, the branch circuits L20 of which connect in the grid circuits of said respective control tubes.

At MO is a low frequency oscillator, the output of which has va potentiometer R in series with a dropping resistance R4 at the input termi- 4 nal of said common lead X9, a capacitance C5 being connected in shunt with said lead, as shown. A flow frequency oscillator answering my re-- quirements is found at page 181 of the publication entitled U'EH Techniques, by Brainerd.

The master oscillator tubes Ml, M2, etc., for? the first stages of the respective cascades, A1,. A2, etc., of the multivibrator waveform genera-- tors are each thereof connected in a. tank cir-- cult T which is individual thereto and includes: a lead L2! connecting the plate of a respective control tube to the control grid of an associated. master oscillator. In series with said lead arecapacitances C2 and C3. A capacitance Cl is connected in shunt with said tank circuit and has a terminal point of connection between capacitances C2 and C3, the opposite terminal of said capacitance connecting with a variable inductance Ll between the field coils thereof. A terminal of one coil of said inductance connects with said lead LEI between capacitances C2 and C3, and, as illustrated, a terminal of the other coil of said inductance is connected in the cathode circuit of a respective master oscillator by an adjustable feelback resistance RI and with the suppression grid of said master oscillator by a lead L3.

The low frequency oscillator MO may be anyof several types such as one of the simpler R.-C.. types, provided the output waveform is substantially sinusoidal. The rate is adjusted to approximately 6 cycles per second although manual. control of the vibrato rate may in some instances be controlled as desired. The extent of the frequency sweep is under control by adjust-- ment of the aforementioned potentiometer R5 in the output of said low frequency oscillator.

Resistance R4 is of the order of magnitude of 209,000 ohms and prevents the grids of the control tubes from swinging appreciably above their respective cathodes and at the same time, avoids possible overloading of the lowfrequency oscillator during its positive swing. Capacitance C5 which is connected in shunt with lead X9 is of the order of magnitude of 0.1 microfarad and functions as a filter to reduce the higher harmonics which tend to be produced during the positive portion of the cycle when the grids of said control tubes rise slightly above their respective cathodes, at which time, the plate resistance of said tubes are at their lowest value as is true also of the frequencies of the master oscillators. Both cathode and grid bias are eliminated by passing the plate supply to the control tubes through resistance R6 in the main plate supply lead P which-is shunted by a large capacitance C6, say 40 microfarads. No change in pitch is in evidence whether the vibrato is on or off. The vibrato is turned off by grounding the output of the lowfrequency oscillator, preferably at the oscillator side of the dropping resistance R4 either by means of a switch or by adjusting potentiometer R5.

The small chokes L2 insure a much greater range in dynamic plate resistance than is possible with the use of resistances. This is due to the fact that a much higher plate voltage is retained, which, in turn, permits a lower plate resistance during the positive swing of the grid voltage cycle.

The design of the master oscillator with its frequency control circuit depends upon the maximum extent desired for the frequency swing. In a frequency vibrato to be used for musical purposes the extent of the frequency sweep, likely,

zgerogvou:

would rarelyexceed per-cent which. is a little less than a semi-tone. This would correspond to a change of approximately lo per cent in either th'einductance or the capacitance-(Ll org-Ci) 'of the; tank circuit as the frequency is inversely proportional to the square root-"of the product of the inductance and the capacitance. It has :been found that if C2 is on the order of 0.1. of Cl, an adequate maximum swing can be obtained, somewhat less than 5 per cent, provided a tube is selected and operated so that its dynamic plate resistance can become as low in magnitude as that of the reactance of C2 at the frequency of the master oscillator concerned.

In selecting the proper values, the choke L2 should have a reactance several times that of G2 at the oscillator frequency. For a given tube, VI, the optimum value of C2 is such that its reactance equals the lowest attainable value of the plate resistance of the tube. (Optimum is used in the sense that the greatest frequency change is possible with this value.) Should this optimum value of C2 be too high a percentage of Cl the tube selected will more than handle the maximum desired frequency swing and consequently C2 can be reduced. If, on the other hand, the optimum value of C2 is too small a percentage of CI, either the oscillator must be redesigned using a smaller Cl and a larger inductance, or a tube having a lower plate resistance must be used.

Assume as a design example that a 6807 or (7E7) triode section is to be considered as the control tube along with a master oscillator operating at a frequency of 3000 cycles per second. Without drawing appreciable grid current, at zero bias, the lowest attainable plate resistance is about 40,000 ohms with a plate voltage of 150 volts. In order, then, for the reactance of C2 to equal 40,000 ohms C2 would be about 0.0013

microfarad. This means that Cl should be about ten times as much or about 0.013 microfarad. The oscillator inductance Ll can be designed now to provide the proper frequency. In the plate lead of the control tube for choke L2 a midget 10-henry choke would be adequate as it would have a reactance of nearly 200,000 ohms at the oscillator frequency. The input on the grid of VI should be great enough to swing the grid from zero bias to or near to the cut-off bias, for maximum vibrato, and less swing as desired.

The values given in the example above are intended to point out the approximate design only. In construction it is not necessary to design closely. To come somewhere nea the design value usually is quite satisfactory.

For locking the multivibrators it has been found that there is an optimum potential which will provide best looking. The optimum potential is obtained readily by adjustment of the potentiometers R3 to which the multivibrators are connected through capacitances C4.

From the foregoing description, it follows that in combination with electron discharge devices producing audio signals at the tone frequencies of notes of the even tempered musical scale and comprising twelve cascades of said devices, the devices comprising each separate cascade will each thereof operate at an invariable frequency, each individual device of any cascade operating at a frequency one-half that of the preceding device of the same cascade. By reason of the embodiment herein of a low frequency oscillator having an output common to all tubes Vi, V2-VI 2, the output frequencies of which are controlled tion-ofth'e: tankcircuits in which said master oscillators are connected, the rate of the vibrato can be changed as desired andwill be the same any place .in the gamut ofthe instrument.

What I claim as my invention-is:

1. In a vibrato organization for electrical musical instruments, the combination comprising twelve frequency dividing circuits, said dividing circuits each embodying a plurality of space discharge devices adapted to produce frequencies at octave separation corresponding to the vibration frequencies of notes of the same letter in the even tempered musical scale; each of said space discharge devices having an output path provided with a selectively actuable electric switch adapted to be controlled from the playingkey of a keyboard; a master oscillator for and individual to each separate dividing circuit for transmitting a controlling frequency to the highest frequency stage thereof; and means for producing a vibrato effect in the output waves of all of said dividing circuits, said means embodying a low frequency oscillator and a set of high vacuum control tubes connected in circuit with said low frequency oscillator and concurrently activated thereby, and means including tuned resonant tank circuits connected with said master oscillators of the respective dividing circuits and with said control tubes and capacitative circuits for periodically shunting said tank circuits during alternate changes in the effective resistance of said control tubes and changes of voltage on the grids thereof.

2. A vibrato comprising a master oscillator embodying a high vacuum tube having at least a plate, a control grid, and a cathode; a high vacuum control tube having a plate and a control grid; a tank circuit in which said master oscillator is connected, said tank circuit including a path connecting the plate of the control tube with the control grid of said master oscillator, said control tube having an impedance adapted to connect the plate of said tube with a plate supply source; the aforementioned path having condensers in series therein, a variable inductance in said tank circuit and including field coils and a capacitance in shunt therewith at a point between said series condensers and having a terminal connected to a terminal of one of the field coils, the other field coil of said variable inductance connected to the cathode of said master oscillator by a feed-back resistance, and an output circuit for said master oscillator, the same provided with an adjustable impedance.

3. A vibrato comprising a master oscillator embodying a high vacuum tube having at least a plate, a control grid, and a cathode; a high vacuum control tube having a plate and a control grid; a tank circuit in which said master oscillator is connected, said tank circuit including a path connecting the plate of the control tube with the control grid of said master oscillator,

said control tube having an impedance adapted to connect the plate of said tube with a plate supply source; the aforementioned path having condensers in series therein, a variable inductance in said tank circuit and including field coils and a capacitance in shunt therewith at a point between said series condensers and having a terminal connected to a terminal of one of the field coils, the other field coil of said variable inductance connected to the cathode of said master oscillator by a, feed-back resistance, and an output circuit for said master oscillator.

file of this patent:

UNITED STATES PATENTS MERWIN J. LARSEN. Number Name Date 2,126,682 Hammond Aug. 9, 1938 REFERENCES CITED 5 2,128,367 Kock Aug. so, 1938 The following references are of record in the 2,328,282 Koch Aug. 31, 1943 2,348,585 Antalek May 9, 1944 am-w... 

